Activity-dependent intracellular Ca2+ transients in unmyelinated nerve fibres of the isolated adult rat vagus nerve.
Confocal laser scanning microscopy was used to follow changes in the free intracellular calcium concentration ([Ca2+]i) in nerve fibres and adjacent Schwann cells in isolated rat vagus nerves. [Ca2+]i was monitored by the Ca2+-sensitive fluorescent dyes Calcium Green-1 and Fura Red. Intracellular Ca2+ transients were observed during repetitive (1-50 Hz) supramaximal electrical stimulation or by bath application of ATP. Trains of action potentials were more effective at elongated, fibre-like structures of the vagus nerves, whereas ATP-induced Ca2+ transients were found predominantly in regions of Schwann cell bodies. Activity-induced Ca2+ signals were unaffected by pharmacological manipulation of intracellular Ca2+ stores, during long-lasting application of purinergic receptor agonists, or by substitution of extracellular Na+ with Li+. However, they were abolished in the presence of Ca2+-free bathing solution or after the blocking of Ca2+ channels with Cd2+. Ca2+ transients were also observed during Ca2+ action potentials. Such "Ca2+ spikes" were elicited by electrical stimulation in the presence of a combination of tetrodotoxin and K+ channel blockers. These data suggest that voltage-dependent Ca2+ channels, activated during short trains of Na+ action potentials, produce an increase in intra-axonal [Ca2+] of rat vagus nerves. We did not find evidence for activity-dependent Ca2+ transients in the Schwann cells surrounding the unmyelinated axons.
Wächtler
J
J
Physiologisches Institut, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 12, D-80336 Munich, Germany.
Mayer
C
C
Grafe
P
P
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D015640:Ion Channel Gating; D008297:Male; D018613:Microscopy, Confocal; D009186:Myelin Sheath / Q000502:physiology*; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D000255:Adenosine Triphosphate; D002211:Capsaicin; D002118:Calcium